Machinery parts that undergo sliding and/or rotating actions require lubrication in order to maintain opposing surfaces separate, minimize friction and provide a cooling effect. Lubricants may also assist in cleaning the working area, preventing corrosion and providing a means of hydro-mechanical energy transfer. Lubricating oils or greases therefore play an important role in prolonging machine life and extending the periods between maintenance.
Moreover, in recent years, along with the advances made in machine technology, materials technology and machining precision, fatigue failure and damage to materials has reduced significantly, so the lifespan of machinery is greatly influenced by the performance of the lubricating oil or grease. Thus, enhancing the lubricating properties of the grease, and solving the problems associated therewith, may make a significant contribution to the raising of the quality and reliability of machinery.
The particular use and performance characteristics of the machinery in which a grease is to be used will determine the desired properties of the grease. For example, in mining and quarrying applications, it is necessary to provide excellent wear protection and long bearing life in relation to slow-moving but heavily loaded bearings and linkages, operating at high temperatures and subject to shock loads. Often, mining and quarrying operations are carried out in extreme environments, such as in regions exposed to sustained sub-zero temperatures, which may have a prevailing wet or dry climate, or in desert-like regions, etc. All these factors have to be taken into account in providing a grease composition that will perform well under the various internal and external influences.
Particularly useful greases are based upon a combination of lubricating oil and a complex soap. Complex soaps are frequently used as grease thickeners and offer superior temperature resistance as compared to their simple soap counterparts. Typically, complex soaps are derived from at least two dissimilar fatty acids, usually a combination of a short chain fatty acid soap and a long chain fatty acid soap. Such soaps may be made by saponification of a metallic hydroxide with the particular fatty acid(s), often taking place in a portion of the lubricating base oil whilst the mixture is blended or otherwise agitated to initiate the reaction. Once the soap has been formed, the balance of the lubricating base oil can be added. One or more additives may be introduced, depending on the desired properties of the final grease composition.
Aluminium complex greases are especially useful being easy to pump at low temperatures and are known to have good reversibility properties, that is, they have the ability to revert to normal consistency after being heated and cooled repeatedly. Another benefit of aluminium complex greases is their superior water-resistance, both in terms of resistance to washing out of a bearing and being washed off a substantially flat surface.
Particular challenges exist when lubricating open gear machinery that is subject not only to extreme ambient temperatures, but also extreme operating conditions. Thus aluminium complex greases are required to be modified by incorporation of one or more additives in order to provide a desired balance of properties for use in such machinery.
Accordingly, it is an object of the present invention to provide an improved aluminium complex grease composition for use in open gear machinery, such as in excavators and shovels used in the mining industry, especially to address the aforementioned challenges of creating a grease composition that performs to a high level under extreme pressure, displaying the requisite balance of wear and weld load properties.